Well, I think wicking is not that it is leaking through the PUL, but that the insert is soooooo full, that the moisture has to go somewhere, so it "wicks" (travels) through the fleece to the next absorbant thing (e.g. clothing). Or, if it is a dipe w/ a cotton outside (e.g. PUL backed), it can wick onto the outside absorbant part of the dipe, and then onto the clothing.

If you are finding your dc's clothes are wet often, it may be that your dipes are repelling (not going through the fleece to the insert) - instead the pee is just rolling of the fleece and it has to go somewhere! If it seems the insert is not soaked, but she is still wet on the outside, you may need to strip!